1. Field of the Invention
This invention relates generally to swivel assemblies which are intended to conduct a pressurized fluid such as a liquid or gas between a first conduit and a second conduit which is approximately coaxial with the first conduit and has relative rotation with respect to the first conduit, and which may have dynamic runout relative to the first conduit and may have static offset relative to the first conduit. More particularly, the present invention is directed to a swivel assembly incorporating a unique sealing mechanism which accomplishes hydrodynamic lubricant pumping activity and permits the swivel mechanism to control the flow of high pressure abrasive fluids and to maintain efficient lubrication at the various sealing interfaces thereof and to thus significantly enhance the service life of the swivel mechanism.
2. Description of the Prior Art
Conventional drilling rig swivels use a stack of redundant rotary seals which are typically of a reinforced elastcmeric chevron type. These seals run against the relatively rotating hardened surface coating of a washpipe. In most designs the washpipe is stationary, and the seals and their housing rotate. The stack of seals is exposed to the high pressure drilling fluid on one side, and to atmospheric pressure on the other. The stack of seals provides redundancy, but since only one seal at a time is exposed to the high pressure differential between the drilling fluid and atmosphere, the pressure capacity of the unit is limited to that of the weakest link, which is the rotary seal. The high differential pressure causes the seal adjacent to the high pressure to grab tightly against the rotating washpipe, and the high interfacial contact pressure causes a high degree of wear on the washpipe and the seal. The high differential pressure and dynamic runout of the application, and the relatively large clearances required to accommodate the dynamic runout, also cause extrusion damage to the seal which contributes significantly to it's ultimate failure. the Once the first seal fails, the next one in the stack is exposed to the high pressure drilling fluid, and so on until all seals have been consumed by the severe operating conditions. Because of the trend toward higher pressure in oilfield drilling (in some cases 7,500 psi or more), the pressure capacity and service life of conventional swivels is in many instances no longer satisfactory. The majority of drilling swivel failures in the field are the direct result of rotary seal failure, and the non-drilling time required to repair the swivel inflates overall drilling costs.